Self-leveling piercing sensor in a fiber optic cable connector

Abstract

A device for detecting a piercing signal during a laser cutting process, comprising a fiber optic cable connector with housing (3) a. with an aperture formed by a fiber bond (8) or holder for receiving a radiation-carrying optical fiber (12) of an optical fiber, which is arranged inside the optical fiber connector, for separating radiation arriving at the output end of the optical fiber connected to the optical fiber connector from radiation reflected back from the workpiece, and b. with at least two photodetectors (6, 7), wherein i. a first photodetector (6) is arranged in the area of ​​the entry of the optical fiber (12) into the housing (3) of the optical fiber connector at the output end of the connected optical fiber for measuring the radiation arriving at the output end of the optical fiber connected to the optical fiber connector, and ii. a second photodetector (7) in a detector shield (4) is connected via a non-concentrically arranged opening (9) in the housing (3) of the fiber optic cable connector to the side separated by the aperture from the output end of the fiber optic cable connected to the fiber optic cable connector, for measuring the radiation reflected back from a workpiece.

Description

Field of the invention

[0001] The invention relates to a sensor arrangement / evaluation that allows power-, pulse frequency- and pulse length-independent piercing detection within a fiber optic cable connector. Description of the relevant state of the art

[0002] Process control is becoming increasingly important in the laser processing of metals or other materials. Particularly when cutting highly structured sheet metals that require frequent piercing, reliable piercing detection can significantly reduce processing times. This is because, in this case, the sum of all piercing processes accounts for a significant portion of the total processing time. Piercing sensors are used to minimize these times. These typically utilize the laser and / or process light reflected from the workpiece. Current state-of-the-art solutions detect the reflected light at various points.

[0003] For example, the light reflected by the optical fiber is measured in the laser or at the coupling point in a fiber optic cable. This signal is transmitted to the system control system. Since the system control system knows the preselected laser power and any pulse parameters, this highly fluctuating signal can be evaluated. The signal propagation time plays a significant role, since piercing procedures are usually performed in pulsed mode.

[0004] Photodetectors beneath the workpiece detect passing laser radiation. Combined with a back-reflection sensor within the laser, this method allows for two opposing signal changes occurring in quick succession to detect a successful piercing. This method already allows for control without precise knowledge of the laser parameters. However, it is disadvantageous that signal patterns depend on the positioning of the photodetectors beneath the workpiece. Furthermore, previously cut-out areas of the workpiece can allow stray light to pass through to the detectors, negatively impacting the signal-to-noise ratio. Typically, the area beneath the workpiece is exposed to heavy contamination, causing the detectors to become contaminated. This also negatively impacts the signal-to-noise ratio.

[0005] Within the cutting optics, a portion of the radiation reflected from the workpiece is redirected by a mirror onto a photodetector. If the evaluation electronics of the cutting optics do not work together with the laser and the system control system, the process parameters are not available and cannot be used to interpret or classify the signals. Therefore, material penetration can only be determined from the temporal progression over a certain period of time, for example, the last five pulses.

[0006] However, according to the Nyquist-Shannon sampling theorem, the sampling frequency used to detect laser pulses must be more than twice the laser's pulse frequency. In practice, however, significantly higher clock rates will be required to detect signals as accurately as possible. This places high demands on signal processing and transmission. Despite considerable effort in signal processing, only changes that are at least five times slower than the laser's pulse frequency can be detected, as it is necessary to look back sufficiently far to reliably detect an event. Furthermore, fluctuations in the beam angle of the laser light from the optical fiber, contamination on lenses, protective glass, or on the end cap surface of the fiber optic cable can generate significant stray light within the cutting optics, thus negatively impacting the signal-to-noise ratio.

[0007] European patent EP 2 795 282 B1 discloses an evaluation of laser process signals within a fiber optic cable connector for quickly shutting down the laser in the event of damage or significant degradation of the fiber optic cable. It also refers to a possible use for quality control and process control in the broadest sense.

[0008] The analysis according to EP 2 795 282 B1 uses scattered laser light that is guided from the optical space of the fiber optic cable connector via a capillary arranged concentrically to the fiber into the rear area of ​​the connector. There, the scattered light from the optical space of the connector as well as the scattered light emerging radially from the fiber is measured with three photodetectors, each of which detects different wavelength ranges (UV, VIS, IR). However, a direct conclusion about the origin of the scattered light is not possible. Therefore, with this method, without knowledge of the laser parameters, with the IR-sensitive photodetector alone, it is not possible to distinguish between laser light coming from the laser and laser light reflected from the workpiece.Only the additional evaluation of other wavelengths by UV / VIS-sensitive photodetectors enables a distinction, since wavelengths other than the laser wavelength (apart from the pump wavelength of the laser) will essentially be process light emitted by the workpiece.

[0009] Furthermore, EP 2 795 282 B1 discloses the possibility of distinguishing between laser light coming from the laser and laser light reflected from the workpiece by comparing the scattered light signals from the input-side fiber optic cable connector with those from the output-side fiber optic cable connector. This is possible because, although backscattered light from the process is present at both connectors, the signal level at the output-side fiber optic cable connector will be higher. However, exploiting this behavior for piercing detection requires fast signal transmission and signal correlation between both connectors with a temporal resolution of less than or equal to 10 ms. This significantly increases the cost of a piercing sensor integrated into the fiber optic cable.

[0010] Published Japanese Patent Application JP 2007-44739 A discloses a laser processing monitoring device comprising an optical fiber for laser transmission, a laser beam detector for monitoring, and a reflected beam detector mounted on the upper surface of a laser processing head. A beam diffusion plate diffuses the radially outgoing beams from a curved mirror, which is a portion of the laser beams emitted from the end face of the optical fiber at a random angle relative to the incident angle, and allows the beams to pass backward. The beam passing through the beam diffusion plate becomes a diffused beam with a radially uniform power density distribution in a beam passage, and a portion of the diffused beams is incident on the beam receiving surface of the beam detector.Also in a reflected beam measurement system, a beam scattering plate has the same effect as the beam scattering plate with respect to the reflected laser beam from a workpiece.

[0011] Published Japanese patent application JP H02-165886 A discloses a device comprising laser light output from a laser oscillator, which is split into working laser light and detection laser light by a beam splitter. The laser light is directed onto an integrating sphere and controls an output of the laser oscillator. The laser light begins to act on an object to be processed, and a portion of the reflected light is transmitted through the beam splitter and detected by a high-speed photoelectric element. A signal indicating the presence of reflected light is output to a piercing monitor.When a hole passes through the object to be machined, no more reflected light is received, therefore a signal is issued indicating that there is no reflected light, and the machining is immediately switched to cutting machining by a command from the device.

[0012] Published US patent US 4,777,341 A discloses a beam monitor comprising a mirror for reflecting an incident beam toward a target and receiving a reflected beam from the target, and having a surface upon which the beams impinge. Channels for incident and reflected beams are arranged orthogonally within the mirror. Each of the channels has an opening in the surface to admit the associated beam. First and second detectors are operatively connected to the mirror and each generate a signal indicative of a selected characteristic of the beam illuminating the associated channel. A controller compares the generated signals and thereby monitors at least one selected characteristic of the target or the beam.

[0013] The published US application US 2018 / 0188544 A1 discloses methods, devices and systems for perturbing a laser beam propagating in a first section of a fiber to adjust one or more beam properties of the laser beam in the first section of the fiber or a second section of the fiber or a combination thereof, coupling the perturbed laser beam into a second section of the fiber and maintaining at least a portion of one or more adjusted beam properties in a second section of the fiber.

[0014] The object of the present invention is therefore to provide a sensor arrangement which is capable of delivering a power-, pulse frequency- and pulse length-independent piercing signal, whereby no sensor is to be used outside the beam guidance system, consisting of laser, coupling optics, fiber optic cable or processing optics. Brief description of the invention

[0015] The present invention provides a device for detecting a piercing signal during a laser cutting process, comprising a fiber optic cable connector with housing a. with a diaphragm formed by a fiber bond or holder for receiving a radiation-carrying optical fiber of a fiber optic cable, which is arranged within the fiber optic cable connector, for separating radiation arriving at the output end of the fiber optic cable connected to the fiber optic cable connector from radiation reflected back from the workpiece, and b. with at least two photodetectors, where i. a first photodetector is arranged in the region of the entry of the optical fiber into the housing of the optical fiber connector at the output end of the connected optical fiber cable for measuring the radiation arriving at the output end of the optical fiber cable connected to the optical fiber connector, and ii. a second photodetector in a detector shield is connected via a non-concentrically arranged opening in the housing of the fiber optic cable connector to the side separated by the aperture from the output end of the fiber optic cable connected to the fiber optic cable connector for measuring the radiation reflected back from the workpiece.

[0016] In a further embodiment of the device according to the invention, it can comprise a circuit for correlating the measured radiation for detecting a laser piercing process.

[0017] Furthermore, according to the invention, it can be provided that the circuit for correlating the measured radiation is arranged within the fiber optic cable connector.

[0018] In a further aspect of the device according to the invention, the circuit for correlating the measured radiation can be a comparator circuit.

[0019] Furthermore, the circuit for correlating the measured radiation can be connected to a signal conductor, which can be a bus system. The signal conductor and / or bus system can be connected to a control unit of the laser cutting process, so that the process can be controlled depending on the result of the correlation of the signals from the first and second photodetectors.

[0020] In a further embodiment of the device according to the invention, at least one photodetector can be connected to a rear part of the fiber optic cable connector via an opening arranged non-concentrically to the optical element supplying radiation.

[0021] In a further embodiment, the opening can be closed by means of an optically transparent element to prevent the entry of dust or moisture into the fiber optic cable connector.

[0022] It is further envisaged that the optical element may be an optical fiber, a lens or a glass cylinder.

[0023] The invention further relates to a method for determining a piercing signal during a laser cutting process, comprising the steps a. Measurement of radiation arriving at the output end of a fiber optic cable connected to a fiber optic cable connector by means of a first photodetector arranged in the region of the entry of the fiber optic fiber into the housing of the fiber optic cable connector at the output end of the connected fiber optic cable, wherein a fiber bond or holder of the radiation-supplying fiber optic cable within a fiber optic cable connector is used as a diaphragm to separate radiation arriving at the output end of the fiber optic cable connected to the fiber optic cable connector and radiation reflected back from the workpiece, and b. Measurement of radiation reflected back from the workpiece by means of a second photodetector in a detector shield, which is connected via a non-concentrically arranged opening in the housing of the fiber optic cable connector to the side separated by the aperture from the output end of the fiber optic cable connected to the fiber optic cable connector.

[0024] In a further aspect, the method may comprise the step of correlating the signals of the measured radiation of the first and second photodetectors in the fiber optic cable connector by means of a comparator circuit.

[0025] Furthermore, the result of the correlation of the signal of the measured radiation in front of and behind the aperture can be fed to a control unit of the laser cutting process by means of a first signal conductor, wherein the first signal conductor can be a BUS system.

[0026] Furthermore, the radiation measured by the two photodetectors can be used to generate a piercing signal.

[0027] According to the invention, in a further embodiment of the method, a piercing signal, i.e. the result of the correlation of the signals of the measured radiation by the first and second photodetector, is transmitted by means of a second signal conductor within the optical fiber cable.

[0028] Additional aspects, features, and advantages of the present invention will be readily apparent from the following detailed description, which simply shows preferred embodiments and implementations. The present invention is capable of being embodied in other and different embodiments, and its several details are capable of modification in various obvious aspects without departing from the spirit and scope of the present invention. Accordingly, the drawings and descriptions are to be regarded as illustrative and not restrictive. Additional objects and advantages of the invention will be set forth in part in the following description and in part will be obvious from the description, or may be learned by practice of the invention. Short description of the characters

[0029] The invention is described in more detail below with reference to the figures. It will be apparent to those skilled in the art that these are only possible exemplary embodiments, without limiting the invention to the embodiments shown. It shows: Fig. 1 shows a schematic structure of a fiber optic cable connector according to the invention. Fig. 2 a schematic representation of useful radiation and process scattered radiation. Fig. 3 Signal waveforms of a fiber optic piercing detector with adjusted gain of the first detector in cw operation. Fig. 4 Signal traces of a fiber optic piercing detector with adjusted gain of the first detector in pulse mode. Fig. 5 Signal curves of the LLK piercing detector in cw operation. Fig. 6 Signal curves of the LLK piercing detector in pulse mode. Detailed description of the invention

[0030] The above-stated object of the invention is achieved by the features of the independent claims. The dependent claims cover further specific embodiments of the invention.

[0031] The invention provides a device which is capable of quickly and reliably detecting a piercing performed during a laser cutting process using only two photodetectors within a fiber optic cable connector, regardless of the set laser parameters.

[0032] For the purposes of the present invention, a fiber optic cable connector is understood to mean a connection for fiber optic cables, preferably a plug-in connection. One part of a plug-in connection can have a receptacle or female part, while the other part of a plug-in connection can have a male part. Fiber optic cable connectors are used to connect fiber optic cables or the ends of fiber optic cables, so that optical radiation from one fiber optic cable or the fiber optic cable arranged therein is coupled into the fiber optic cable of another fiber optic cable.

[0033] According to the invention, this is achieved by using the fiber bond as a near-field aperture to carry out a signal separation between the radiation coming from the laser (hereinafter referred to as useful radiation) and the radiation that is reflected back from the workpiece (hereinafter referred to as process scattered radiation).

[0034] A key advantage of the present invention is that, in contrast to signal correlation between the input and output fiber optic cable connectors, as known from the prior art, the analog signal processing already takes place within a fiber optic cable connector, eliminating the need for rapid signal correlation over many meters between the input and output fiber optic cable connectors. The correlation of the scattered light signals takes place within a fiber optic cable connector. Only the piercing signal resulting from this correlation needs to be transmitted to the higher-level system control system via a signal conductor, e.g., a BUS system. This allows the frequency of the transmitted signal to be considerably lower than that required for correlating two scattered light signals. This transmission can take place within the fiber optic cable.

[0035] Fig. Figure 1 shows the schematic structure of a device according to the invention in one embodiment of a fiber optic cable connector with a housing 3 that is cooled. For this purpose, cooling water flows through the cooling water supply line 10 to the cooling water return line 11, both of which are arranged within the housing 3 of the fiber optic cable connector.

[0036] At one end of the housing 3 of the fiber optic cable connector, the optical fiber 12 is guided into the housing 3, surrounded by a fiber optic cable protection tube 1. A first detector 6, e.g., a photodetector, for measuring scattered light 2 of the useful light is arranged in the area where the optical fiber 12 enters the housing 3 of the fiber optic cable connector.

[0037] At the opposite end of the fiber optic connector is its receptacle, for example, for another fiber optic connector or the optics of a laser material processing head. The optical fiber 12 is centrally positioned or held in place in the fiber optic connector by means of a fiber centering device 13. Furthermore, the optical fiber 12 is held in place by the fiber bonding 8 in the housing of the fiber optic connector at the inner end of the receptacle of the fiber optic connector. The centering of the optical fiber 12 can also be achieved by means of an end cap (not shown) spliced ​​to the optical fiber.

[0038] An opening for process scattered light 9 is arranged next to the fiber bond 8, as the fiber bond 8 rests against the housing 3 of the fiber optic cable connector 3, thus sealing it tightly against the opening of the receptacle in this area of ​​the fiber optic cable connector. On the side of the opening 9 for process scattered light facing away from the receptacle of the fiber optic cable connector 3, a second detector 7, e.g., a photodetector, for measuring scattered light 5 of the process scattered light is arranged in a detector shield 4.

[0039] Useful radiation 14 ( Fig. 2) arriving at the output end of the fiber optic cable has already been optically filtered several times. Precise coupling into the fiber core ensures that as little light as possible remains in the fiber cladding. Portions of the useful radiation 14 that have been coupled into the fiber cladding are attenuated by cladding mode strippers. Bonding the fiber 8 at the input further reduces the remaining radiation. Portions of the useful radiation 14 that have been coupled into the core but whose numerical aperture is too large to be guided by the optical fiber 12 also leave the core and experience corresponding attenuation in the fiber cladding. This also applies to residual radiation in the fiber cladding that can no longer be guided by the fiber cladding. This portion is broken out of the optical fiber over the length of the fiber optic cable – typically 20 m or more.

[0040] Useful radiation 14, which leaves the fiber optic cable on the output side, passes through optical systems of the processing optics 18 and then hits the workpiece surface 19 as a focused laser beam 20. From there, the process scattered radiation 17 ( Fig. 2), which couples into the fiber cladding at the output end of the fiber optic cable. Process scattered radiation 17, which couples in or violates the boundary conditions for guidance in the fiber core, also experiences significant attenuation, comparable to that at the input end. The scattered light signal 2 ( Fig. 1) behind the fiber bond 8 ( Fig. 1) of the output-side fiber optic cable connector will only be slightly increased by this process scattered radiation 17. Therefore, a relatively clean scattered light signal will be found in the output-side fiber optic cable connector if a first detector 6 ( Fig. 1) is positioned at this point. The situation is completely different in the area before the fiber bonding 8. Process scattered radiation 17, which couples into the fiber cladding, is deflected by means of a cladding mode stripper from the optical fiber into the absorber area of ​​the fiber optic cable connector 15 ( Fig. 2).

[0041] Process scattered radiation 17, which neither hits the fiber core nor the fiber cladding, reaches the absorber area 16 ( Fig. 2). There it is absorbed by absorbing surfaces and usually by an active water cooling system with cooling water supply and cooling water return 10, 11 ( Fig. 2). The scattered light level will therefore be many times higher in the absorber area 15 of the fiber optic cable connector in the event of process scattered light than behind the fiber bond 8. The fiber bond 8 acts as a near-field diaphragm. A comparably effective separation of useful and process scattered radiation 14, 17 is found only at this point in the entire optical transmission chain from the active laser medium to the workpiece. Therefore, if one measures with a second photodetector 7 ( Fig. 1) Scattered light in the absorber area 15 of the output-side fiber optic cable connector 5 ( Fig. 1), one will generally measure mainly process scattered light 17. Since - with respect to the fiber optic cable - the essential attenuation mechanisms for this process scattered light 17 take place in this absorber area 15, this scattered light signal reacts very sensitively to any type of reflection from the workpiece.

[0042] However, fluctuations in this signal depend not only on the occurrence of process scattered radiation 17. A key influencing factor is the absolute level of effective power radiated onto the workpiece and its temporal progression. For example, if the signal level of process scattered radiation 17 in the absorber area 15 suddenly increases by a factor of 3, without knowledge of the absolute level of the radiated effective power, it is impossible to determine whether this was caused by three times higher backscattering or three times higher radiated effective power.

[0043] The same applies to pulsed laser operation, which is typically present during the piercing process. Here, the useful power fluctuates at high frequency between 0 W and several thousand W. However, if the scattered light signal from the first photodetector 6 is used to determine the magnitude of the useful signal and its temporal progression and this information is correlated with the scattered light signal from the second photodetector 7, this allows an evaluation of the process scattered radiation even without knowledge of the laser parameters, since the respective reference value is part of the measuring system and is always determined synchronously. The first photodetector 6 can also be used to filter the signal from the second photodetector 7 if its signal is used as the input of an amplifier circuit. In this way, interfering noise signals can be suppressed.

[0044] For evaluation, a simple analog circuit with operational amplifiers is recommended. With appropriate signal pre-amplification and a comparator circuit, a signal curve for piercing detection could be generated, as in Fig. 3 and Fig. 4. A threshold is set using the gain factors. A signal curve for piercing detection using the quotient of both signals is shown. Fig. 5 and Fig. 6. The threshold value would be set here via the quotient. Since the evaluation is analog, complex computing power and fast bus systems are largely eliminated. Only the threshold value is configured digitally via the LLK's internal bus. However, this bus can be significantly slower and does not need to maintain a 10 ms clock rate. The comparator output, for example, can be used to feed back the piercing signal.

[0045] In order not to impair the installation space for cooling the absorber area of ​​the fiber optic cable connector and to avoid unnecessary temperature fluctuations of the sensor, it is expedient to arrange the second photodetector 7 also in the rear area of ​​the fiber optic cable connector in such a way that it is shielded against stray light from the rear connector area and temperature influences from the front area by means of a detector shield 4 ( Fig. 1).

[0046] The supply of scattered light from the absorber area is expediently carried out through an opening 9 which is not arranged concentrically to the optical fiber ( Fig.1). Only a non-concentric arrangement of the opening allows light to be transported without affecting the bonding / mounting of the light-carrying optical fiber. This allows heat to continue to dissipate from this bonding point. If, for example, a capillary were used concentrically to the light-carrying optical fiber, the fiber bond would inevitably be thermally insulated. This significantly limits the use of the fiber optic cable for high and very high laser powers. It is particularly advantageous to close this opening with a transparent material, such as glass, or with another optical fiber to prevent dust or similar substances from entering the absorber area.Since even the smallest deposits of dust or other contaminants on the cladding area of ​​the optical fiber in the absorber area would immediately lead to the failure of the entire fiber optic cable, tightly closing this opening is essential for the long-term function of the fiber optic cable.

[0047] The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be learned from practice of the invention. The embodiment was chosen and described in order to explain the principles of the invention and their practical application to enable one skilled in the art to utilize the invention in various embodiments suited to the particular use contemplated. It is intended that the scope of the invention be defined by the appended claims and their equivalents. The entirety of each of the above-referenced documents is incorporated herein by reference. Reference symbol 1 fiber optic cable protection tube 2 Scattered light at detector 1 3 Housing fiber optic cable connector 4 Detector shielding 5 Scattered light at detector 2 6 first detector - useful light 7 second detector - process scattered light 8 Fiber bonding / holder 9 Opening for process scattered light detection (sealed with fiber) 10 Cooling water supply 11 Cooling water return 12 optical fibers 13 Fiber centering 14 Useful light from the laser to the workpiece 15 Absorber area of ​​the fiber optic cable connector 16 Process scattered radiation guided from the fiber and radiated next to the fiber 17 Process stray light from the workpiece to the fiber optic cable connector 18 Optical system of the processing optics 19 Workpiece surface 20 Focused laser beam within the workpiece

Claims

[1] A device for detecting a piercing signal during a laser cutting process, comprising a fiber optic cable connector with a housing (3) a. with a diaphragm formed by a fiber bond (8) or holder for receiving a radiation-supplying optical fiber (12) of a fiber optic cable, which is arranged within the fiber optic cable connector, for separating radiation arriving at the output end of the fiber optic cable connected to the fiber optic cable connector from radiation reflected back by the workpiece, and b. with at least two photodetectors (6, 7), wherein i. a first photodetector (6) is arranged in the region of the entry of the optical fiber (12) into the housing (3) of the optical fiber connector at the output end of the connected optical fiber for measuring the radiation arriving at the output end of the optical fiber connected to the optical fiber connector, and ii. a second photodetector (7) in a detector shield (4) is connected via a non-concentrically arranged opening (9) in the housing (3) of the fiber optic cable connector to the side separated by the aperture from the output end of the fiber optic cable connected to the fiber optic cable connector, for measuring the radiation reflected back from a workpiece. [2] The apparatus of claim 1, further comprising a circuit for correlating the measured radiation to detect a laser piercing event. [3] The apparatus of claim 2, wherein the circuit for correlating the measured radiation is disposed within the fiber optic cable connector. [4] The device according to any one of claims 2 or 3, wherein the circuit for correlating the measured radiation is a comparator circuit. [5] The device according to any one of claims 2 to 4, wherein the circuit for correlating the measured radiation is connected to a signal conductor. [6] The device according to claim 5, wherein the signal conductor is a BUS system. [7] The device according to claim 5 or 6, wherein the signal conductor or BUS system is connected to a control unit of the laser cutting process. [8] The device according to one of claims 1 to 5, wherein at least one photodetector is connected to a rear part of the fiber optic cable connector via an opening arranged non-concentrically to the radiation-supplying optical element. [9] The device according to claim 6, wherein the opening is closed by an optically transparent member to prevent the entry of dust or moisture into the fiber optic cable connector. [10] The device according to claim 6 or 7, wherein the optical element is an optical fiber, a lens or a glass cylinder. [11] A method for determining a piercing signal during a laser cutting process comprising the steps a. Measurement of radiation arriving at the output end of a fiber optic cable connected to a fiber optic cable connector by means of a first photodetector (6) arranged in the region of the entry of the fiber optic fiber (12) into the housing (3) of the fiber optic cable connector at the output end of the connected fiber optic cable, wherein a fiber bond (8) or holder of the radiation-supplying fiber optic fiber (12) of the fiber optic cable within a fiber optic cable connector is used as a diaphragm for separating radiation arriving at the output end of the fiber optic cable connected to the fiber optic cable connector and radiation reflected back from the workpiece; and b. Measurement of radiation reflected back from the workpiece by means of a second photodetector (7) in a detector shield (4) which is connected via a non-concentrically arranged opening (9) in the housing (3) of the fiber optic cable connector to the side separated by the aperture from the output end of the fiber optic cable connected to the fiber optic cable connector. [12] The method according to claim 11, wherein the signals of the measured radiation of the first and second photodetectors in the fiber optic cable connector are correlated by means of a comparator circuit. [13] The method according to one of claims 11 or 12, wherein the result of the correlation of the signals of the measured radiation of the first and second photodetectors is fed to a control unit of the laser cutting process by means of a first signal conductor. [14] The method of claim 13, wherein the first signal conductor is a BUS system. [15] The method according to claim 13, wherein the control unit controls the laser cutting process depending on the transmitted signal. [16] The method according to any one of claims 11 to 15, wherein the radiation measured by the two photodetectors is used to generate a piercing signal. [17] The method of claim 16, wherein a piercing signal is transmitted by means of a second signal conductor within the fiber optic cable.

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